1. Field of the Invention
The present invention relates to an exposing apparatus and an exposing method, for maskless exposure of a substrate to be exposed, and a plotter and plotting method for directly plotting on an object to be plotted.
2. Description of the Related Art
In the manufacturing process of a wiring substrate, a resist film, that is, a photosensitive resin film, is formed on the substrate, the resist is exposed into a desired pattern, and the desired pattern is formed by etching processing. In recent years, however, a maskless exposing method, that is, a method for exposing without using a photomask has been proposed because the above-mentioned method uses a photomask and the cost is accordingly higher.
As an example of a maskless exposing method, Japanese Unexamined Patent Publication (Kokai) No. 10-112579 has disclosed a technique for exposing a resist formed on a substrate, in which pattern data in accordance with the pattern to be exposed is formed, the pattern data is input to a digital micro-mirror device (DMD), each of a plurality of infinitesimal mirrors is tilted in accordance with the pattern data, a ray of light is projected on the DMD and the resist is irradiated with reflected light from each infinitesimal mirror, and thus a desired exposure pattern, in accordance with the pattern data, is formed.
On the other hand, Japanese Unexamined Patent Publication No. 2001-174721 has disclosed a technique, for various plotters using a DMD, in which the DMD, made up of infinitesimal mirrors capable of tilting independently of each another, is arranged between a laser light source and a laser scanner and a laser beam is reflected on the DMD for plotting.
In the DMD, a plurality of infinitesimal mirrors are arranged at predetermined intervals. The light projected onto the DMD is reflected by the infinitesimal mirrors of the DMD and the substrate to be exposed is irradiated therewith. In the meantime, the substrate to be relatively exposed moves at a predetermined speed with respect to the infinitesimal mirrors, that is, the light source, and undergoes the exposing processing sequentially.
FIG. 5 is a diagram for explaining the positional relationship between the substrate to be exposed and the light source.
It is assumed that the number of times the turning-on and turning-off of the light source P can be switched per unit time is F. In the present specification, this F is referred to as a frame rate. It is also assumed that the relative distance covered by the movement of the substrate to be exposed with respect to the light source, during the period of time corresponding to one frame, that is, during the time required for determining whether the light source P is turned on or left in the unlit state at the next timing, is S. In the present specification, this S is referred to as a step size.
In FIG. 5, a case where spot A and spot B at a distance r from each other on the substrate to be exposed are discriminated and irradiated with the light from the light source P is explained as an example.
It is assumed that the spot A is exposed by the light source at a point of time when the substrate to be exposed moves in the positive direction of the x-axis. The coordinate of the spot A on the x-axis is assumed to be the origin O.
During the period of time required for determining whether the light source P is turned on or left in the unlit state at the next timing, that is, during the period of time corresponding to one frame, the substrate to be exposed travels the distance S with respect to the light source P. Therefore, if the spot B to be exposed after the spot A is apart from the spot A only by the distance r shorter than the distance S along the direction of the relative movement of the light source P, the light source P will pass beyond the spot B (the position of the light source P is denoted by the circle drawn by the dotted line) when the period of time corresponding to one frame elapses after the spot A is exposed, therefore, the spot B cannot be exposed. In other words, when the step size S is longer than the distance r between the neighboring spots to be exposed, that is, when r<S, a desired exposing process cannot be carried out. In other words, when the distance r between the neighboring spots to be exposed is beyond the ability to control the turning-on of the light source in an exposing system, the desired exposing process cannot be carried out. Hereinafter, the distance r between the neighboring spots is referred to as the resolution.
As described above, the finer the exposing pattern on the substrate to be exposed, the finer the resolution r needs to be.
By the way, when the distance r between the neighboring spots to be exposed is shorter than the interval of the light sources, conventionally, the substrate to be exposed is moved relatively with respect to the row of two or more light sources arranged in a two-dimensional pattern at an angle to the direction perpendicular to the direction of the relative movement with respect to the light source P on the substrate to be exposed.
In contrast to this, as to the direction of the relative movement with respect to the light source P on the substrate to be exposed, one possible solution is that the moving speed of the substrate to be exposed with respect to the light source P is reduced, that is, the step size S is reduced. However, if the step size S is reduced in order to carry out the exposing process with a fine resolution r, the exposing speed (throughput) is reduced. From the standpoint of the exposing speed and productivity, it is preferable that the step size S is as large as possible.
As described above, the fact that, on one hand, a fine resolution r is maintained and, on the other hand, the exposing speed is increased, that is, the step size S is increased contains two incompatible prepositions essentially. It seems that the demand in the industrial field for finer exposing patterns and for higher speeds of exposing process will become stronger in the near future. Therefore, a solution is expected for an exposure in which even when the distance (that is, resolution) r between neighboring spots is shorter than the step size S, in other words, even when r<S, a desired resolution r and step size S can be maintained.
The above-mentioned problem is not limited to the maskless exposing apparatus using the DMD, but significantly relates to a plotter such as an ink-jet plotter in which a plurality of ink-jet heads are arranged at predetermined intervals and which carry out the plotting process while an object to be plotted moves relatively with respect to the ink-jet heads.
Therefore, the object the present invention is, the above-mentioned problem being taken into account, to provide an exposing apparatus and an exposing method capable of efficiently irradiating with light even a row of spots having the distance between neighboring spots to be irradiated shorter than the distance covered by the relative movement of a substrate to be exposed during one period of the shortest turning-on controllable period of the light source, and to provide a plotter and a plotting method capable of efficiently plotting even a row of spots having a distance between neighboring spots, to be plotted, shorter than the distance covered by the relative movement of an object to be plotted during one period of the shortest head controllable period of the plotting head.